This invention relates to a clutch-brake unit of the type in which an input member and an output member are coupled to rotate in unison when a friction shoe is moved into frictional engagement with and is turned by the input member. The invention more specifically relates to a clutch in which the friction shoe may be engaged with relatively low force and in which the force acting on the friction shoe is amplified to enable the clutch to possess relatively high torque capacity.
An amplifying clutch of this general type is disclosed in MacDonald U.S. application Ser. No. 151,340, filed May 19, 1980, entitled Amplifying Clutch With Radially Contractible Shoe and assigned to the assignee of the present invention. In that clutch, turning of the friction shoe by the input member creates a pilot torque which is used to contract a helical spring. The spring amplifies the pilot torque by wrapping down on a series of angularly spaced shoe segments and causing the shoe segments to radially grip the input member and transmit torque of substantial magnitude to the output member.
The friction shoe is adapted to be moved out of engagement with the input member by a braking ring. The braking ring applies a retarding torque to the output member when the braking ring is moved to disengage the friction shoe from the input member.